1. Field of the Invention
This invention relates in general to radio frequency (RF) shielding for a room and more particularly to a personnel swing door sealing system which eliminates the need for a step or ramp at the entrance to the room.
2. Discussion of the Prior Art
In general it is necessary to provide shielding at any apertures of a room having a significant source of RF radiation. Alternatively, in certain applications, the room will need to be shielded from an outside RF source. Such shielded rooms are used, for example, for circuit testing for RF emission tests, for housing certain computer installations, etc. A shielded room of the type to which the present invention is directed is usually a specially made enclosure and is of sufficient size to permit passage of workmen and technicians therethrough. A primary problem with construction of such a shielded enclosure is to provide a personnel access door which will completely seal against electromagnetic radiation leakage while affording the least obstruction to personnel passage therethrough.
The above described rooms having a source of RF radiation require effective sealing systems around all openings to avoid leakage of electromagnetic radiation. In the present art, shielding around a personnel door is provided by a series of shielding plates fixed around the border of the door. The shielding plates are metallic and to minimize RF leakage contact the door frame of the aperture or the wall of the shielded room all around the personnel door. A typical example of a RF shielded door seal can be found in U.S. Pat. No. 4,370,831 issued to Hamilton. Obviously a "step" above floor level is required to gain access into the shielded room if the door is a swing type door as its bottom must be sealed against the door frame or wall to provide acceptable sealing. If the door were to extend all the way to the floor and no sealing surface counter to the lower part of the door were provided, ineffective shielding would result with gross leaking of electromagnetic radiation. The present art, therefore, requires that the personnel access aperture of a swing door not extend to floor level. A surface counter to the door must be provided all the way around the borders of the door to effect a positive RF seal. This requirement results in a "step" above floor level at the personnel access aperture which provides an obstruction of facile passage of personnel and equipment therethrough. The step can be hidden by a ramp on one or both sides of the access aperture, however, the ramp is obviously a hindrance relative to free access to the room. It is therefore highly desirable to provide a personnel swing door which suitably seals against RF radiation leakage and does not have any obstructions to traffic flowing in or out. It should be noted that the "step" can be eliminated if the door is a sliding type door with a track set below the floor opening. This type of door, however, requires more space and is generally more expensive than a swing door. The present invention eliminates the foresaid problems and improves upon the present art as will become evident from the following summary of the invention.